Method for increasing vacuum production for a vehicle

ABSTRACT

Methods and systems for providing vacuum to a vehicle are described. In one example, a method adjusts an application force of a transmission clutch in response to a request for additional vacuum.

FIELD

The present description relates to methods and systems for operating anengine that produces vacuum for a vehicle. The methods and systems maybe particularly useful for engines that are boosted and that operate athigh altitudes.

BACKGROUND AND SUMMARY

Vehicle engines may be downsized to conserve fuel and reduce engineemissions. Smaller engines may operate more frequently at higher intakemanifold pressures as compared to larger engines in the same vehicle.Engine pumping losses may be reduced by operating an engine with higherintake manifold pressures, but the opportunities to provide enginevacuum to the vehicle vacuum system may be reduced. Some attempts toincrease vacuum production have included ejectors, ways ofadvantageously controlling engine throttle position, and various othercontrol strategies. However, many of these systems and methods requirehardware that is additional to more conventional engines. Consequently,vehicle cost may be higher for such systems.

The inventors herein have recognized the above-mentioned disadvantagesand have developed a method for operating a vehicle powertrain,comprising: reducing torque delivered from an engine to vehicle wheelsvia reducing a torque transferred via a clutch in response to a requestfor increased vacuum.

At very low vehicle speed (e.g. less than 6 to 10 kph), torque or forceproduced by a vehicle engine tends to purposefully accelerate a vehiclewhile the operator's foot is off the accelerator pedal. This is calledcreep force. By reducing an amount of engine torque that is provided tovehicle wheels (creep torque) when no driver demand torque is present,it may be possible to provide a technical result of an engine providingan increased amount of vacuum for vacuum consumers. For example, if anengine is operating at idle speed and X Nm of torque is provided by theengine to vehicle wheels to maintain a positive torque at the wheels, itmay be possible to reduce engine torque from X Nm to Y Nm whilecontinuing to operate the engine at the same idle speed such thatadditional intake manifold vacuum is produced. In particular, since lessengine torque is used to operate the engine at Y Nm than at X Nm, theengine can operate using a reduced air charge, and the reduced aircharged is provided via throttling the engine and allowing less air intothe engine intake manifold so that intake manifold pressure is reducedand vacuum is increased. In this way, the desired technical result ofproviding additional vacuum may be achieved.

The present description may provide several advantages. Specifically,the approach may improve an amount of vacuum available for a vehicle.Further, the approach may not be noticeable to a driver. In addition,the approach may reduce an amount of time that it takes an engine toproduce a desired amount of vacuum.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages described herein will be more fully understood by readingan example, referred to herein as the Detailed Description, when takenalone or with reference to the drawings, where:

FIG. 1 is a schematic diagram of an engine;

FIG. 2 is shows an example powertrain system layout;

FIG. 3 is an example schematic diagram of a transmission clutch;

FIG. 4 is a plot of an example engine operating sequence; and

FIG. 5 is a flowchart of an example powertrain control method.

DETAILED DESCRIPTION

The present description is related to providing vacuum for vacuumconsumers of a vehicle. In one non-limiting example, slip of atransmission input clutch is increased in response to a request forincreased vacuum. Engine load may be reduced by increasing transmissionclutch slip so that the engine may provide additional vacuum. In oneexample, the engine may be as illustrated in FIG. 1. Further, the enginemay be part of a vehicle powertrain as illustrated in FIG. 2. FIG. 3shows an example transmission input clutch for an Automatically ShiftedManual (ASM) transmission. In one example, the transmission input clutchmay be electrically actuated. However, in other examples, thetransmission input clutch or clutches may be hydraulically actuated.FIG. 4 shows an example operating sequence when the method of FIG. 5 isexecuted via a controller as shown in FIGS. 1 and 2.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53. Theposition of intake cam 51 may be determined by intake cam sensor 55. Theposition of exhaust cam 53 may be determined by exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to the pulse width of signal FPW fromcontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).Fuel injector 66 is supplied operating current from driver 68 whichresponds to controller 12. In addition, intake manifold 44 is showncommunicating with optional electronic throttle 62 which adjusts aposition of throttle plate 64 to control air flow from intake boostchamber 46.

Compressor 162 draws air from air intake 42 to supply boost chamber 46.Exhaust gases spin turbine 164 which is coupled to compressor 162 viashaft 161. Vacuum operated waste gate actuator 72 allows exhaust gasesto bypass turbine 164 so that boost pressure can be controlled undervarying operating conditions. Vacuum is supplied to waste gate actuator72 via vacuum reservoir 138. Vacuum reservoir 138 may be supplied vacuumfrom intake manifold 44 via intake manifold vacuum flow control valve 24and check valve 60. Intake manifold vacuum flow control valve 24 isoperated via an electrical signal from controller 12. In some examples,check valve 60 may be omitted.

Vacuum reservoir 138 may also be supplied vacuum via ejector 20. Ejectorvacuum flow control valve 22 may be opened to permit compressed air fromcompressor 162 to pass through ejector 20. Compressed air passes throughejector 20 and creates a low pressure region within ejector 20, therebyproviding a vacuum source for vacuum reservoir 138. Air flowing throughejector 20 is returned to the intake system at a location upstream ofcompressor 162. In an alternative example, air flowing through theejector 20 may be returned to the air intake system via conduits to theintake manifold at a location downstream of throttle 62 and at alocation upstream of compressor 162. In the alternative configuration,valves may be placed between the outlet of ejector 20 and intakemanifold 44 as well as between the outlet of ejector 20 and air intake42. Check valve 63 ensures air does not pass from ejector 20 to vacuumreservoir 138. Air exits ejector 20 and reenters the engine air intakesystem at a location upstream of compressor 162.

While ejector 20 is useful for increasing intake manifold vacuum andincreasing vacuum level, it may not have capacity to provide as muchvacuum as is desired in a short amount of time. Further, the performanceof ejector 20 may be reduced during times when accelerator pedal 130 isnot depressed or when engine torque demand is low since vacuum providedby ejector 20 increases as air flow through ejector 20 increases.Consequently, it may be desirable to increase intake manifold vacuum viaa plurality of control actions including reducing and/or eliminatingcreep torque while providing vacuum via ejector 20. In this way, ejector20 may provide even deeper vacuum to the vehicle vacuum system.

Vacuum reservoir 138 provides vacuum to brake booster 140 via checkvalve 65. Vacuum reservoir 138 may also provide vacuum to other vacuumconsumers such as turbocharger waste gate actuators, heating andventilation actuators, driveline actuators (e.g., four wheel driveactuators), fuel vapor purging systems, engine crankcase ventilation,and fuel system leak testing systems. Check valve 61 limits air flowfrom vacuum reservoir 138 to secondary vacuum consumers (e.g., vacuumconsumers other than the vehicle braking system). Brake booster 140 mayinclude an internal vacuum reservoir, and it may amplify force providedby foot 152 via brake pedal 150 to master cylinder 148 for applyingvehicle brakes (not shown).

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 via spark plug 92 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupled toexhaust manifold 48 upstream of catalytic converter 70. Alternatively, atwo-state exhaust gas oxygen sensor may be substituted for UEGO sensor126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing accelerator positionadjusted by foot 132; a position sensor 154 coupled to brake pedal 150for sensing brake pedal position; a knock sensor for determiningignition of end gases (not shown); a measurement of engine manifoldpressure (MAP) from pressure sensor 121 coupled to intake manifold 44; ameasurement of boost pressure from pressure sensor 122 coupled to boostchamber 46; an engine position sensor from a Hall effect sensor 118sensing crankshaft 40 position; a measurement of air mass entering theengine from sensor 120 (e.g., a hot wire air flow meter); and ameasurement of throttle position from sensor 58. Barometric pressure mayalso be sensed via sensor 183 for processing by controller 12. In apreferred aspect of the present description, engine position sensor 118produces a predetermined number of equally spaced pulses everyrevolution of the crankshaft from which engine speed (RPM) can bedetermined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof. Further, in some examples, other engine configurations may beemployed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is described merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

FIG. 2 is a block diagram of a vehicle powertrain 200. Powertrain 200may be powered by engine 10. Engine 10 may be started with an enginestarting system (as shown in FIG. 1). Further, engine 10 may generate oradjust torque via torque actuator 204, such as a fuel injector, airinlet throttle, etc. ASM transmissions slip clutch 206 to mimic thecreep torque provided historically from automatic transmissions withtorque converters or fluid couplings.

An engine output torque may be transmitted to transmission input clutch206 to drive automatically shifted manual transmission 208 viatransmission input shaft 236. Clutch 206 may be comprised of one or moresets of clutch discs and one or more pressure plates as shown in FIG. 3.Further, one or more gears 230 coupled to first layshaft 278 or secondlayshaft 277 may be selectively engaged to propel a vehicle. In oneexample, the clutch 206 may be referred to as a component of thetransmission. The position of clutch 206 may be adjusted to varyapplication force applied to clutch 206 to couple engine 10 toautomatically shifted manual transmission 208. Clutch 206 may beelectrically or hydraulically actuated.

Torque output from the automatically shifted manual transmission 208 mayin turn be relayed to wheels 216 to propel the vehicle via transmissionoutput shaft 234. Specifically, automatically shifted manualtransmission 208 may transfer an input driving torque at the input shaft236 responsive to a vehicle traveling conditions before transmitting anoutput driving torque to the wheels.

If the ASM stops producing a creep torque, it may be advantageous forthe brake system to provide a torque that opposes vehicle reverse motionif the transmission is in a forward gear and opposes vehicle forwardmotion if the transmission is in a reverse gear. The brake system mayincrease brake system pressure during such conditions. Effectively, thevehicle brakes may function as a directional ratchet mechanism. It maydo this in a number of ways, but one method is to arrange thetransmission or wheel brakes to be self-actuating such that the intendedmotion is opposed with far less torqued than is the unintended motion.Further, a frictional force may be applied to wheels 216 by engagingwheel brakes 218. In one example, wheel brakes 218 may be engaged inresponse to the driver pressing his foot on a brake pedal (not shown).In the same way, a frictional force may be reduced to wheels 216 bydisengaging wheel brakes 218 in response to the driver releasing hisfoot from a brake pedal. Further, vehicle brakes may apply a frictionalforce to wheels 216 as part of an automated engine stopping procedure.

Gear clutches 230 may be selectively applied via gear actuator 233. Gearactuator 233 may be electrically or hydraulically operated. Clutch 206may be set to an open state when gear actuator 233 shifts betweendifferent gear ratios.

Transmission input speed may be monitored via transmission input shaftspeed sensor 240. Transmission output speed may be monitored viatransmission output shaft speed sensor 244. In some examples,inclinometer 250 may provide vehicle road grade data to controller 12 sothat clutch 206 may be controlled (e.g., increase or decrease clutchapply pressure and adjust clutch engagement timing) via controller 12.In some examples, torque transmitted through transmission 208 may bedetermined via a torque sensor 245.

A controller 12 may be configured to receive inputs from engine 10, asshown in more detail in FIG. 1, and accordingly control a torque outputof the engine and/or operation of the torque converter, transmission,clutches, and/or brakes. As one example, a torque output may becontrolled by adjusting a combination of spark timing, fuel pulse width,fuel pulse timing, and/or air charge, by controlling air inlet throttleopening and/or valve timing, valve lift and boost for turbo- orsuper-charged engines. In the case of a diesel engine, controller 12 maycontrol the engine torque output by controlling a combination of fuelpulse width, fuel pulse timing, and air charge. In all cases, enginecontrol may be performed on a cylinder-by-cylinder basis to control theengine torque output.

In some examples, wheel brakes 218 may be held in an applied state aftera driver releases a brake pedal and before a threshold driver demandtorque is provided. By holding the state of wheel brakes 218, it may bepossible to reduce the possibility of the vehicle rolling when thedriver releases the brake on a hill.

In alternative examples, transmission 208 may be an automatictransmission including a plurality of gear clutches 230. If transmission208 is an automatic transmission 206 is a torque converter instead of anautomated clutch. Creep may be reduced in an automatic transmission viaslipping a gear clutch 230. For example, if the vehicle is stopped agear clutch (e.g., 1^(st), 2^(nd), 3^(rd), or 4^(th) gear clutch) may beslipped to reduce creep torque.

The system of FIGS. 1 and 2 provide for a system for operating a vehiclepowertrain, comprising: an engine; a transmission coupled to the enginethat includes an electrically actuated clutch; and a controllerincluding executable instructions stored in a non-transitory medium toreduce an application force of the electrically actuated clutch inresponse to a request for vacuum. The system includes where the requestfor vacuum is based on a pressure in a vacuum canister. The systemfurther comprises an inclinometer, and additional executableinstructions to determine road grade from the inclinometer. The systemfurther comprises additional instructions for adjusting the applicationforce (which in turn controls the creep force) in response to roadgrade. The system further comprises additional instructions foradjusting the application force in response to an altitude at which theengine is operated. The system includes where the engine includes aturbocharger, and additional instructions to adjust the applicationforce in response to road grade when a vehicle brake is not applied.

Referring now to FIG. 3 an example clutch 206 is shown. Transmissioninput clutch 206 includes friction discs 318 that apply force totransfer torque to shaft 340 via spline 346. Damper spring 322 reducesoscillations through the transmission when force is applied to frictiondiscs 318. Electric motor 302 rotates screw 304 and causes roller 308 tomove linearly in the directions of arrows 350. Roller 308 acts on lever312 to adjust the position of pressure plate 316 as indicated by arrows352. Return spring 306 applies force opposing the force applied byelectric motor 302 to lever 312 via roller 308. In this way, returnspring 306 releases pressure plate 316 from applying force to frictiondiscs 318 when roller 308 is in the position shown. Lever 312 transfersforce from electric motor 302 to pressure plate 316 via engagementbearing 320.

Referring now to FIG. 4, a sequence showing example operation of themethod of FIG. 6 in the system of FIGS. 1 and 2 executed viainstructions stored in non-transitory memory of controller 12. Verticalmarkers at times T₀-T₈ indicate particular areas of interest during thesequence.

The first plot from the top of FIG. 4 is a plot of vehicle brake stateversus time. The X axis represents time and time increases from the leftside of the figure to right side of the figure. The Y axis representsvehicle brake state and the vehicle brake is applied when the vehiclebrake state trace is at a higher level. The vehicle brake is not appliedwhen the vehicle brake state trace is at a lower level.

The second plot from the top of FIG. 4 represents a vacuum requesttrace. The X axis represents time and time increases from the left sideof the figure to right side of the figure. The Y axis represents vacuumrequest (e.g. additional vacuum requested) and vacuum is requested whenthe vacuum request trace is at a higher level. Vacuum is not requestedwhen the vacuum request trace is at a lower level.

The third plot from the top of FIG. 4 represents road grade versus time.The X axis represents time and time increase from the left side of thefigure to the right side of the figure. The Y axis represents road gradeand road grade is positive above the X axis and it increases in thedirection of the Y axis arrow.

The fourth plot from the top of FIG. 4 represents vehicle speed versustime. The X axis represents time and time increases from the left sideof the figure to the right side of the figure. The Y axis representsvehicle speed and vehicle speed increases in the direction of the Y axisarrow.

The fifth plot from the top of FIG. 4 represents the transmission inputclutch application force command. The X axis represents time and timeincreases from the left side of the figure to the right side of thefigure. The Y axis represents the transmission input clutch applicationforce command and the transmission input clutch application forcecommand increases in the direction of the Y axis arrow. The greater thetransmission application force the greater amount of engine torque istransferred from the engine to the transmission.

At time T₀, engine speed is constant and transmission input clutchapplication force is at a higher level. Road grade is zero and no vacuumis presently being requested. The brake state is low indicating that thevehicle brake is not applied.

At time T₁, the vehicle brake is applied by a driver (not shown) and thevehicle speed begins to decrease in response to the brake application.Application of the vehicle brake consumes vacuum from a vacuumreservoir. The road grade and vacuum request remain at zero and notasserted. The transmission input clutch application force remains at ahigher level.

Between time T₁ and time T₂, the vehicle speed continues to decrease andthe transmission input clutch application torque is shown increasing anddecreasing as the transmission is downshifted in response to vehiclespeed and driver demand torque. The vehicle brake remains in an appliedstate and the vacuum request remains low and not asserted so thatadditional vacuum is not requested. As vehicle speed approaches zero thetransmission input clutch application torque is reduced to a base levelthat is sufficient to propel the vehicle at a low speed (e.g., less than8 Km/hr) when the vehicle brake is not applied and when the vehicle istraveling on a road with zero grade. The transmission input clutchapplication torque is changed in response to vehicle speed and driverdemand torque.

At time T₂, the vehicle reaches a stopped state and the road grade andvacuum request remain at zero and not asserted. The brake remainsapplied by the driver and the transmission input clutch applicationforce remains at the base level.

At time T₃, the vehicle brake is released and the transmission inputclutch application force increases with an increasing driver demandtorque (not shown). The road grade is zero and the vacuum requestremains not asserted.

Between time T₃ and time T₄, the vehicle accelerates and thetransmission input clutch is applied and released as the transmission isshifted. The road grade remains at zero and the vacuum request remainsnot asserted. The brake is not applied.

At time T₄, the vehicle brake is applied and vehicle speed begins to bereduced. The transmission input clutch application torque decreases andincreases as the transmission is downshifted in response to vehiclespeed and driver demand torque. The road grade remains at zero and thevacuum request remains not asserted.

Between time T₄ and time T₅, the transmission input clutch applicationforce is decreased and increased several times as the transmission isdownshifted in response to vehicle speed and driver demand torque. Thevehicle speed continues to decline and the vacuum request remains notasserted. As vehicle speed approaches zero, the transmission inputclutch application force is reduced to the base application force inresponse to vehicle speed and driver demand torque.

At time T₅, the vacuum request is asserted (e.g., transitions to ahigher level) in response to a pressure in a vacuum reservoir (notshown). This measured vacuum may be either the brake booster vacuum, avacuum reservoir, a node in the vacuum harness, or the engine intakemanifold vacuum. Thus, the vacuum system is requesting vacuum to powervacuum consumers such as the brake booster. The transmission inputclutch application torque is reduced in response to the request forvacuum. By reducing the clutch application torque, less engine torque isused to rotate the engine at idle speed so that less air is drawn intothe intake manifold, thereby producing additional vacuum for the vacuumsystem. The road grade remains at zero and the brake remains applied.

When a vehicle is braked and stopped, the operator may not sense thelevel of creep torque (except for tertiary effects) because brakeapplication force far exceeds the creep torque. Thus, the first time anoperator may sense a reduced level of creep is upon releasing the brakeand before applying the accelerator. If vacuum is replenished to adesired level before a driver releases the brake, the base level ofcreep force (e.g., a creep force provided when vacuum is not requested)may be restored.

Between time T₅ and time T₆, the transmission input clutch applicationtorque remains at a reduced level and the engine provides vacuum to thevacuum system. In conditions where the engine is capable of providingvacuum when the transmission input clutch application torque is at abase level, the engine vacuum is increased. The brake remains appliedand the vacuum request remains asserted.

At time T₆, the brake pedal is released and the transmission inputclutch application torque is increased to a level that is below the basetransmission input clutch application torque in response to releasingthe brake pedal. The transmission input clutch application torque isincreased to reduce driveline gear lash and to provide a small torque tothe wheels. The engine produces vacuum at a reduced level as comparedbetween time T₅ and time T₆; however, vehicle driveline lash may bereduced and vehicle acceleration may be improved.

Between time T₆ and time T₇, the transmission input clutch applicationforce is increased and decreased several times as the transmission isshifted in response to increasing vehicle speed and driver demand torque(not shown). The vacuum request remains not asserted and the vehiclebrake is not applied. The road grade increases and then stabilizes at alevel greater than zero. The road grade is positive indicating that thevehicle is traveling up hill.

At time T₇, the driver applies the vehicle brake and the vehicle beginsto decelerate. The vacuum request remains not asserted and the roadgrade remains at the elevated level.

Between time T₇ and time T₈, the transmission input clutch applicationforce is decreased and increased as the transmission is downshifted inresponse to vehicle speed and driver demand torque (not shown). Thetransmission input clutch application force is also reduced to a baselevel as vehicle speed approaches zero. The road grade remains positiveand elevated.

At time T₈, the vacuum request is asserted in response to a low vacuumlevel in a vacuum reservoir. However, with a slow or stopped vehicle,when the vehicle is traveling uphill in a forward gear, a low vacuum inthe brake booster may not be an issue since the grade opposes vehicleforward motion. It may be desirable to reduce the possibility of thevehicle rolling backwards. Thus, base creep torque is provided ratherthan trying to address a possible booster vacuum deficiency. The same istrue for going uphill in reverse gear. On the other hand, if the vehicleis traveling downhill in the direction of transmission selecteddirection (e.g., forward gear), vacuum is increased via reducing creeptorque from base creep torque (e.g., zero creep torque).

Further, the amount or magnitude of creep torque is adjustable inresponse to road grade. For example, if the road grade is a positivesteeper grade and the vehicle is in a forward gear and headed uphillwhile vacuum is requested, the base creep is provided. If the road gradeis a positive middle level grade and the vehicle is in a forward gearand headed uphill while vacuum is requested, the creep torque is reducedfrom the base creep torque (e.g., ⅔ of the base creep torque isprovided). If the road grade is a positive lower level grade and thevehicle is in a forward gear and headed uphill while vacuum isrequested, the base creep is reduced further approaching zero creep(e.g., ⅕ base creep torque). On the other hand, if the road grade is anegative steeper grade and the vehicle is in a forward gear and headeddownhill while vacuum is requested, the base creep may be reduce agreater amount (e.g., zero creep). If road grade is a negative middlegrade and the vehicle is in a forward gear and headed downhill whilevacuum is requested, the base creep torque is reduced less (e.g., 1/16creep torque is provided). If road grade is a negative lower grade andthe vehicle is in a forward gear and headed downhill while vacuum isrequested, the base creep torque is reduced even less (e.g., ⅛ creeptorque is provided). Similar actions may be provided for operating thetransmission in reverse and traveling up or down hill. If vacuum is notrequested, the base creep torque may be provided.

In this way, creep torque may be selectively adjusted in response toroad grade, transmission gear, and road grade. Additionally, the creepforce in the above examples may be adjusted in response to thedifference between the desired vacuum in the vacuum system and theactual vacuum in the vacuum system. For example, if there is a greaterdifference between the actual system vacuum and the desired systemvacuum while the vehicle is in a forward gear and traveling downhill,the creep force may be reduced an additional amount based on thedifference between desired and actual system vacuum. On the other hand,if there is a less difference between the actual system vacuum and thedesired system vacuum while the vehicle is in a forward gear andtraveling downhill, the creep force may not be reduced an additionalamount based on the difference between desired and actual system vacuum.

As mentioned, creep torque is adjustable for an ASM transmission viaslipping the automatically actuated clutch while creep torque for anautomatic transmission may be reduced via increasing slip of gearclutches. In this way, creep torque is adjustable for mountainconditions.

The transmission input clutch application force is reduced to a levelless than the application force level at time T₂ and more than theapplication force level between times T₅ and T₆. The transmission inputclutch application force is adjusted from the base level based on theroad grade and vacuum request so that the vehicle has less possibilityof rolling in a reverse direction if the brakes are released while theengine is providing vacuum. The vehicle brakes are maintained in anapplied state.

Referring now to FIG. 5, a method for an example powertrain control isshown. The method of FIG. 5 may be executed by the system shown in FIGS.1 and 2 executing instructions stored in non-transitory memory. Themethod of FIG. 5 may provide the sequence shown in FIG. 4.

At 502, method 500 judges whether or not driver demand torque is lessthan a threshold torque request. The driver demand torque may berequested by a driver via an accelerator pedal or other input device. Ifdriver demand torque is less than a threshold torque, the answer is yesand method 500 proceeds to 504. Otherwise, the answer is no and method500 exits. In the simplest case, if the operator is not applying theaccelerator pedal, then 502 returns a yes answer and method 500 proceedsto 504.

At 504, method 500 judges whether or not vehicle speed is less than athreshold speed. Vehicle speed may be determined from a wheel speedsensor or a transmission shaft speed sensor. If vehicle speed is lessthan a threshold speed, the answer is yes and method 500 proceeds to506. Otherwise, the answer is no and method 500 exits.

In some examples, 504 may judge whether to proceed to 506 or exit basedon synchronous speed. If the clutch input shaft and output shaft aregoing at the same speed, they are at a synchronous speed. If the engineside of the clutch is rotating slower than the transmission (vehiclewheel) side, engine braking is performed and method 500 proceeds toexit. If the engine side of the clutch is rotating faster than thetransmission side, engine torque may be applied to the wheels, therebyproducing creep and method 500 proceeds to 506. For an ASM vehicle, theautomatically actuated clutch is adjusted to give a target creepcharacteristic in torque, acceleration, or speed.

At 506, method 500 applies a base application force to the transmissioninput clutch. In one example, the base application force is an amount offorce that allows engine torque to propels the vehicle at apredetermined speed (e.g., less than 8 Km/hr) when the driver demandtorque is zero. In one example, the base application force isempirically determined and stored to memory. Method 500 proceeds to 508after the base application force is an amount of force is applied to thetransmission input clutch.

At 508, method 500 judges whether or not additional vacuum is requestedby the vacuum system. The vacuum system may request additional vacuumwhen pressure in a vacuum reservoir increases to a pressure greater thana threshold pressure. If method 500 judges that there is a request foradditional vacuum, the answer is yes and method 500 proceeds to 510.Otherwise, the answer is no and method 500 proceeds to exit.

At 510, method 500 judges whether or not the vehicle brakes are applied.Output of a brake pedal sensor may be used to determine whether or notthe vehicle brakes are applied. If method 500 judges that brakes areapplied, the answer is yes and method 500 proceeds to 512. Otherwise,the answer is no and method 500 proceeds to 516.

In the 512-514 path, the vehicle motion is controlled by the vehiclebrake and creep torque may be significantly reduced to fulfill thevacuum request. At 512, method 500 determines vehicle altitude and/orbarometric pressure. In one example, method 500 determines barometricpressure via a barometric pressure sensor. In other examples, method 500may determine vehicle altitude via a satellite based global positioningsystem. Method 500 proceeds to 514 after barometric pressure and/orvehicle altitude are determined.

At 514, method 500 adjusts a base transmission input clutch applicationforce in response to the vacuum request and barometric pressure oraltitude. In one example, a difference between a desired vacuum leveland an actual vacuum level is determined via subtracting the presentvacuum level in the vacuum reservoir from the desired vacuum level. Theresult is used to index a table or function that stores empiricallydetermined adjustments to the base transmission input clutch applicationforce. If the difference between the present vacuum level and thedesired vacuum level is small, the base transmission input clutchapplication force is reduced by a small amount so that engine outputtorque is reduced. If the difference between the present vacuum leveland the desired vacuum level is large, the base transmission inputclutch application force is reduced by a larger amount so that engineoutput torque is reduced further than if the difference is small.Reducing the transmission input clutch application force increasesclutch slip and reduces the amount of torque transferred from the engineto the vehicle wheels. Increasing the transmission input clutchapplication force decreases clutch slip and increases the amount oftorque transferred from the engine to the vehicle wheels.

If the engine is being operated near sea level, no adjustments are madeto the base transmission input clutch application force in response tobarometric pressure. If the engine is being operated at a higheraltitude, the transmission input clutch application force is increasedtoward the base transmission input clutch application force when thebase transmission input clutch application force has been reduced inresponse to the vacuum request. The specific amount that thetransmission input clutch application force is adjusted may vary fromapplication to application. Method 500 proceeds to exit after thetransmission input clutch application force is adjusted.

Thus, the transmission input clutch application force may be reduced inresponse to a request for vacuum; however, the reduction in transmissioninput clutch application force may be decreased in response to vehiclealtitude since less air is available at lower barometric pressures. Inthis way, the amount of vacuum that may be provided by the engine may belimited while the engine rotates at a desired idle speed.

At 516, method 500 determines vehicle altitude and/or barometricpressure as described at 512. Additionally, brake force may bedetermined via monitoring brake fluid pressure or brake pedal position.Method 500 proceeds to 518 after barometric pressure and/or altitude aredetermined.

At 518, method 500 determines road grade. In one example, output of aninclinometer is converted to road grade. Road grade is positive for avehicle engaged in a forward gear and traveling uphill. Road grade isnegative for a vehicle engaged in a forward gear and traveling downhill.Method 500 proceeds to 520 after road grade is determined.

At 520, method 500 selects a transmission gear for holding the vehicleon the hill. In one example, the transmission gear is a higher gear than1^(st) gear (e.g., third gear) so that the perceived vehicle massincreases and so that less engine torque is used to hold the vehicle onthe hill. If the driver demand torque increases, the transmission may beshifted to a lower gear to accelerate the vehicle. Method 500 proceedsto 522 after the transmission gear is selected.

At 522, method 500 determines an amount of torque the transmission inputclutch transfers from the engine to the transmission to hold the vehicleon the grade determined at 518.

If the grade is negative, the amount of torque is reduced from basecreep torque toward zero torque depending on the difference betweendesired system vacuum and actual system vacuum as well as the gradelevel or amount estimate. If the grade is positive the wheel torque isdetermined via the following equation:

Tw=RR·Mv·g·sin Θ+Tr

Where: Tw is wheel torque on grade angle θ, RR is driven wheel rollingradius, My is mass of the vehicle, g is acceleration due to gravity, θis the grade angle, and Tr is the road load torque ant the driven wheelon grade angle θ. The torque at the wheel is then adjusted based on thepresently selected transmission gear ratio to determine the transmissioninput clutch hill hold torque to transfer through the transmission inputclutch. In this way, the creep torque is adjusted for grade.Additionally, the wheel torque may be adjusted responsive to adifference in actual vacuum and desired vacuum in the vacuum system asdescribed in FIG. 4. Further, FIG. 4 describes several examples ofadjusting creep torque according to method 500. Additionally, creeptorque may be decreased in response to applied brake force as determinedvia brake line pressure. For example, if applied brake force is greaterthan a threshold brake force, the base creep force may be reduced by afirst amount. If brake force is less than the threshold brake force, thebase creep force may be reduced by a second amount, the second amountless than the first amount. Method 500 proceeds to 524 after thetransmission input clutch hill hold torque is determined.

At 524, method 500 adjusts a base transmission input clutch applicationforce or gear clutch in response to the vacuum request, barometricpressure or altitude, and road grade. In one example, an adjustment tothe base transmission input clutch application force based on the vacuumrequest is determined as described at 514. Further, if the engine isbeing operated near sea level, no adjustments are made to the basetransmission input clutch application force in response to barometricpressure. If the engine is being operated at a higher altitude, thetransmission input clutch application force is increased toward the basetransmission input clutch application force when the base transmissioninput clutch application force has been reduced in response to thevacuum request. The specific amount that the transmission input clutchapplication force is adjusted may vary from application to application.Additionally, the base transmission input clutch application force isadjusted based on the transmission input clutch hill hold torque. Inparticular, the transmission input clutch hill hold torque indexes atable of empirically determined clutch application force values usingthe transmission input clutch hill hold torque and the table outputs anadjustment to the base transmission input clutch application force.Method 500 proceeds to exit after the transmission input clutchapplication force is adjusted.

In this way, the transmission input clutch application force may beadjusted in response to a request for vacuum, altitude, and road grade.In some examples, the vacuum request may be given higher priority thanthe adjustment for road grade so that little if any adjustment isprovided for road grade when additional vacuum is requested.

Thus, the method of FIG. 5 provides for operating a vehicle powertrain,comprising: reducing torque delivered from an engine to vehicle wheelsvia reducing a torque transferred via a clutch in response to a requestto a request for increased vacuum. The includes where the request forincreased vacuum is based on a pressure in a vacuum reservoir. Themethod further comprises operating the engine at an idle speed whilereducing torque delivered from the engine to the vehicle wheels. Themethod includes where the clutch is automatically adjusted via acontroller. The method of claim 1, where the torque transferred via theclutch is reduced via slipping the clutch and reducing a clutchapplication force. The method includes where the clutch is atransmission input clutch. The method further comprises providing vacuumto a vacuum reservoir via an engine intake manifold in response to therequest for increased vacuum.

In another example, the method of FIG. 5 provides for a method foroperating a vehicle powertrain, comprising: delivering a first torquefrom an engine to wheels of a vehicle when the vehicle is stopped in theabsence of a request for vacuum; and delivering a second torque from theengine to the wheels of the vehicle when the vehicle is stopped inresponse to a request for additional vacuum, the second torque less thanthe first torque. The method includes where vehicle brakes are appliedwhile the vehicle is stopped. The method further comprises adjusting thesecond torque in response to an altitude at which the engine is beingoperated. The method further comprises adjusting the second torque inresponse to a grade the vehicle is on.

In some examples, the method includes where the request for vacuum isbased on a vacuum level within a vacuum reservoir. The method includeswhere the second torque is based on a difference between a vacuum levelof a vacuum reservoir and a desired vacuum level. The method includeswhere the first torque and the second torque are delivered to the wheelsof the vehicle via an automatically shifted manual transmission.

Additionally, the method of FIG. 5 provides for method for operating avehicle powertrain, comprising: reducing torque delivered from an engineto vehicle wheels via reducing a torque transferred via a clutch inresponse to a vehicle being engaged in a forward gear and travelingdownhill. The method further comprises reducing torque delivered fromthe engine to the vehicle wheels in response to a request for increasedvacuum, and where the request for increased vacuum is based on apressure in a vacuum reservoir. The method of claim 1, furthercomprising operating the engine at an idle speed while reducing torquedelivered from the engine to the vehicle wheels, and further reducingtorque delivered from the engine to vehicle wheels in response toapplied vehicle brake force. The method includes where the clutch isautomatically adjusted via a controller, and further comprises applyinga base torque delivered from the engine to vehicle wheels in response tothe vehicle being engaged in a forward gear and traveling uphill. Themethod includes where the torque transferred via the clutch is reducedvia slipping the clutch and reducing an clutch application force, andfurther comprises applying a base torque delivered from the engine tovehicle wheels in response to the vehicle being engaged in a forwardgear and traveling on a zero grade road.

As will be appreciated by one of ordinary skill in the art, routinesdescribed in FIG. 5 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas,gasoline, diesel, or alternative fuel configurations could use thepresent description to advantage.

1. A method for operating a vehicle powertrain, comprising: reducingtorque delivered from an engine to vehicle wheels via reducing a torquetransferred via a clutch in response to a vehicle being engaged in aforward gear and traveling downhill.
 2. The method of claim 1, furthercomprising reducing torque delivered from the engine to the vehiclewheels in response to a request for increased vacuum, and where therequest for increased vacuum is based on a pressure in a vacuumreservoir.
 3. The method of claim 1, further comprising operating theengine at an idle speed while reducing torque delivered from the engineto the vehicle wheels, and further reducing torque delivered from theengine to vehicle wheels in response to applied vehicle brake force. 4.The method of claim 1, where the clutch is automatically adjusted via acontroller, and further comprising applying a base torque delivered fromthe engine to vehicle wheels in response to the vehicle being engaged ina forward gear and traveling uphill.
 5. The method of claim 1, where thetorque transferred via the clutch is reduced via slipping the clutch andreducing an clutch application force, and further comprising applying abase torque delivered from the engine to vehicle wheels in response tothe vehicle being engaged in a forward gear and traveling on a zerograde road.
 6. The method of claim 1, where the clutch is a transmissioninput clutch.
 7. The method of claim 1, further comprising providingvacuum to a vacuum reservoir via an engine intake manifold in responseto the request for increased vacuum.
 8. A method for operating a vehiclepowertrain, comprising: delivering a first torque from an engine towheels of a vehicle when the vehicle is stopped in the absence of arequest for vacuum; and delivering a second torque from the engine tothe wheels of the vehicle when the vehicle is stopped in response to arequest for additional vacuum, the second torque less than the firsttorque.
 9. The method of claim 8, where vehicle brakes are applied whilethe vehicle is stopped.
 10. The method of claim 8, further comprisingadjusting the second torque in response to an altitude at which theengine is being operated.
 11. The method of claim 8, further comprisingadjusting the second torque in response to a grade the vehicle is on.12. The method of claim 8, where the request for vacuum is based on avacuum level within a vacuum reservoir.
 13. The method of claim 8, wherethe second torque is based on a difference between a vacuum level of avacuum reservoir and a desired vacuum level.
 14. The method of claim 8,where the first torque and the second torque are delivered to the wheelsof the vehicle via an automatically shifted manual transmission.
 15. Asystem for operating a vehicle powertrain, comprising: an engine; atransmission coupled to the engine that includes an electricallyactuated clutch; and a controller including executable instructionsstored in a non-transitory medium to reduce an application force of theelectrically actuated clutch in response to a request for vacuum. 16.The system of claim 15, where the request for vacuum is based on apressure in a vacuum canister.
 17. The system of claim 15, furthercomprising an inclinometer, and additional executable instructions todetermine road grade from the inclinometer.
 18. The system of claim 17,further comprising additional instructions for adjusting the applicationforce in response to road grade.
 19. The system of claim 18, furthercomprising additional instructions for adjusting the application forcein response to an altitude at which the engine is operated.
 20. Thesystem of claim 15, where the engine includes a turbocharger, andadditional instructions to adjust the application force in response toroad grade when a vehicle brake is not applied.